1. Field of the Invention
The present invention relates generally to coal firing of glass tank furnaces, and more particularly to direct coal firing in which pulverized coal is combusted in the atmosphere immediately over the molten glass.
2. Description of the Prior Art
Coal firing per se has been in existence for many years. Fundamentally, indirect coal firing, i.e., through a heat exchange surface to protect the substance to be heated, is typified by the household furnace of the recent sort. Combustion products from the coal firing were, of course, maintained separate from the heated air. Similarly, a number of other substances have been heated by indirect coal firing. Early glass melting for hand-blown glass was accomplished by indirect heating. The automation of glassware production resulted in the location of glass plants at sites where natural gas was abundant. Thus, for many years gas and oil have been utilized to fuel tank furnaces for glass.
Pulverized coal firing is more conventionally utilized in conjunction with somewhat less demanding processes such as the production of cement, brick firing, metal reduction and steam power generation. Pulverized coal is supplied, usually in a fluidized manner, through a nozzle which functions in a manner somewhat analogous to that of a gas burner. The air utilized to carry the pulverized coal is, during combustion, largely employed to oxidize the coal. The resulting heat may be utilized either directly or indirectly. However, in the former instance, use has been with less sensitive processes such as ore processing, cement kilns, etc. U.S. Pat. No. 1,841,587 illustrates the known apparatus.
Heretofore, it has been almost unanimously accepted that the production of glass in a glass tank furnace was much too dependent upon the atmosphere conditions of the furnace to permit direct pulverized coal firing. For instance, in a "Discussion of Influence of Furnace Atmosphere on the Melting-Firing Rate of Soda-Ash Glasses," Canadian Clay and Ceramics, February, 1973 and S. B. Joshi et al, "The Effects of Gaseous Atmospheres on Factors Affecting Melting and Refining of Glass," 33rd Annual Conference on Glass Problems, Ohio State, 1972, discuss and establish the critical importance of the atmosphere over the melting glass. Further, it is well known that coal contains a substantial ash residue which, being neither volatile nor combustible, would settle into the glass melt.
For these reasons, there appears to be no record of an attempt to utilize direct coal firing to supply or supplement the heat load required for the melting of glass in a glass tank furnace. The glass industry originally located in areas with abundant natural gas. More recently fuel oil and electricity have also been employed to supply the needed energy.